If I'm one on Neptune how old am I on Earth?

If you were on Neptune, your age in Earth years would depend on how long you have lived there. However, if you're asking about the difference in time perception due to Neptune's longer orbital period, Neptune takes about 165 Earth years to complete one orbit around the Sun. Therefore, one year on Neptune would be equivalent to about 0.006 Earth years, or approximately 2.2 Earth days.